Conventionally, tunnel communication, in which target data are encapsulated for communication, has been developed. Such technology is disclosed in Japanese Patent Laid-Open Application No. 2003-244188 (the first and other pages, and the third and other figures).
In tunnel communication, communication target data to be encapsulated also needs its IP address to be set by an information-processing device as a communication terminal. The IP address must be set so as not to overlap among each information-processing terminal. Meanwhile, methods of allocating an address include DHCP and AutoIP.
However, an address allocation method with DHCP, AutoIP or the like uses a heuristic algorithm. In AutoIP, for instance, an address range is set in advance and the following processes are repeated: an information-processing device at the client inquires at the server if a given IP address is available or not. If the address is not being used by another information-processing device, the address is used; otherwise, the device further inquires if still another address is available or not. This heuristic algorithm is complicated and has problems in that it takes a long time to determine an IP address to be used by an information-processing device at the client. Further, an IP address within a predetermined range is allocated by the client's information-processing device so as not to overlap, and thus the device is unable to allocate too many addresses to exceed a predetermined address range.